here is a nested test
\begin{one}[optional argument]
	to be nested to be nested
	to be nested to be nested
	to be nested to be nested
	\begin{two}\[ x^2\]
		nested text nested tex nested tex [not an argument]
		nested text nested tex nested tex
		nested text nested tex nested tex
		nested text nested tex nested tex
	\end{two}
\end{one}
\begin{three}{mandatory argument}
  three text
  three text
  three text
\end{three}
\begin{four}{mandatory argument}{second mandatory}
  four text
  four text
  four text
\end{four}
\begin{five}[optional] {mandatory argument} {second mandatory}\{ something else\}
  five text
  five text
  five text
\end{five}
\begin{six} {mandatory argument}
            [optional] 
            {second mandatory}    [second optional]\{ something else\}   
  six text
  six text
  six text
\end{six}
